146 



PRACTICAL PHYSIOLOGY 



with a wire loop, so that the glass need not be touched with the hand. 

 The animal chamber a light beaker is provided with a thermometer 

 and is also fitted with a wire loop. The moisture given off' by the animal 

 is absorbed by pumice saturated with sulphuric acid in the tubes AB. 

 The pumice is heated red-hot before it is thrown into the acid. The 

 carbon dioxide is removed by soda lime C, the water given off by the 

 soda lime is caught by the sulphuric acid tube D. 



M N A B c D 



FIG. 128. The Haldane-Pembrey respiration apparatus. 



The animal is weighed in the beaker (with the tubes closed) before 

 and after the experiment. A dummy beaker is placed in the opposite 

 scale pan. The tubes AB and CD are also weighed against a dummy 

 pair of tubes. During the weighings the exit and entrance tubes 

 are left unstoppered. By these means errors due to condensation of 

 water and changes of barometric pressure or temperature are avoided, 

 and the weighings can be carried out to less than a milligramme. 



The air entering the chamber is freed from C0 2 and H 2 by soda- 

 lime in M and sulphuric acid pumice in N. The amount of H 2 and 

 C0 2 given off in 15 minutes is determined by the increase in weight 

 of AB and CD respectively. The amount of oxygen absorbed is 

 found by subtracting the loss in weight of the animal weighed in 

 the chamber from the total loss of C0 2 and H 2 0. 



mi x- C0 9 grins. 32 C0 9 by volume 



The ratio ^ 2 & x - = 2 . J -, = respiratory quotient. 



O 2 grms. 44 2 by volume 



The effect of external temperature upon the respiratory exchange 

 may be studied with this apparatus. 



EXAMPLE. The beaker containing a full-grown mouse was placed in 

 water bath at 9'5 C., and then in water bath at 30 C. At 9 -5 C. the 

 mouse gave off from 250-315 decimgrms. of C0 2 per 10 minutes and 

 was active. 



At 30 C. it gave off 103-116 decimgrms. C0 2 per 10 minutes and 

 was quiet. The rectal temperature of the animal scarcely varied during 

 the experiment. New-born mammals in an immature condition behave 

 like cold-blooded animals, and are unable to compensate for low 

 external temperature by increased metabolism. The C0 2 output in 

 them sinks with the body temperature. 



